Various abbreviations that may appear in the description and drawings are defined as follows:    BW bandwidth    ESD electrostatic discharge    FEM front-end module    GSM global system for mobile communications    HB higher band    LB lower band    MEMS microelectromechanical system    S-parameters scattering parameters    S11 input reflection coefficient of 50 Ohm terminated output    S22 output reflection coefficient of 50 Ohm terminated input    SPDT single pole, double throw    UMTS universal mobile telecommunications system    WCDMA wideband code division multiple access
Physically small antennas are a necessity for modern portable electronic devices, including communications devices such as mobile phones. However, as the size of the antenna is reduced it becomes more challenging to provide operation over a bandwidth that includes two or more frequency bands of interest. In general, decreasing the size of the antenna reduces the bandwidth, which in turn decreases the number of possible operating frequency bands. For example, in order to accommodate with one antenna the operating frequency bands in both the European and US cellular frequencies the antenna and related circuitry needs to have wide bandwidth properties.
Conventionally the use of matching components and/or tuning by switching in and out additional ground connections has enabled an increase in the antenna bandwidth. However, as the antenna size is decreased below a certain level the use of these conventional approaches is no longer adequate to achieve the desired bandwidth.
Representative conventional approaches to radio frequency antenna and related circuitry design include US 2005/0181847, “Wireless Terminals”, Kevin R. Boyle, that describes a wireless terminal having a dual band antenna arrangement that comprises a planar inverted-F antenna having a first feed for signals in a first, lower frequency band, for example the GSM band, a second feed for signals in a second, higher frequency band, for example the DCS band, and a ground pin. In operation when transmitting in one of the bands, first and second PIN diodes of a relevant coupling stage are switched-on, while the PIN diodes in the other coupling stage are off, and when in a receiving mode all the PIN diodes are off. The signal being received by one of the transceivers is reflected by a band pass filter in the coupling stage of the other transceiver.
In U.S. Pat. No. 6,229,495 B1, “Dual-Point-Feed Broadband Whip Antenna”, Alfred R. Lopez et al. describes a dual-radiator whip antenna to operate over a 30 to 450 MHz frequency band, and that includes a high frequency dipole above a low frequency monopole. An outer conductor of a coaxial line is configured to operate as a monopole. Above the upper terminus of the outer conductor, an extension of the inner conductor is configured as the upper arm of a dipole. An upper length of the outer conductor also functions as the lower dipole arm. With a single antenna port, a diplexer and other feed elements separate signals into high and low frequency bands respectively coupled to the dipole and monopole radiators. An increased high frequency range is said to result from positioning of the center of radiation of the dipole above the monopole.
Also of interest to multi-band antenna design principles is “Multi-Band Antennas with Integrated Circuitry in Mobile Phones”, L. P. Ligthart, IRCTR-Delft University, LEAT Sophia Antipolis, June 2005, as well as “A Novel Dual-fed, Self-Diplexing PIFA and RF Front-end (PIN-DF2-PIFA)”, K. R. Boyle, M. Udink, A. de Graauw and L. P. Ligthart, Antennas and Propagation Society International Symposium, 2004, IEEE, Volume 2, 20-25 Jun. 2004, pages 1935-1938.
A diplexer is basically a device that enables two radio transmitters to use the same antenna. Existing diplexer designs fail to provide a desired wide bandwidth operation with a small antenna radiator.